1. Field of the Invention
The present invention relates to a method and nodes for efficient localization of traffic in Proxy Mobile IP networks and in other networks using access gateways.
2. Description of the Related Art
Mobile Internet Protocol (IP) is a protocol that provides routing of IP datagram to a mobile node (MN) as it travels through the Internet. The MN has a home IP address, which is used when the MN is located within a home domain. The home domain provides a subscription and the home IP address to the MN. When the MN is located outside of the home domain, it acquires a care-of address from a visited domain. The visited domain informs the home domain of the care-of address allocated to the MN in a so-called binding process. When a packet or datagram is received in the home domain identifying the home address as a destination, while the MN is known to be roaming in the visited domain, the home domain forwards the packet towards the MN in a tunnel, with the care-of address as a new destination address. Mobile IP requires that the MN be capable of detecting whether it is located in the home or in a visited network, and acquiring a care-of address.
Many devices, such as laptops or personal assistants, may be moved by their users, but do not have those capabilities. The user of a mobile device may elect to disable its Mobile IP capability, for example to reduce signaling on a wireless link between the mobile device and an access point of a visited domain.
Proxy Mobile IP (PMIP) provides Mobile IP features to MNs that do not support mobility. With PMIP, the MN does not need to support any mobility related signaling. Mobility features are solely supported by the network. The care-of address that was assigned by a visited network to the MN, in Mobile IP, is replaced in PMIP by a proxy care-of address (pCoA). The pCoA is the address of a gateway that provides connectivity to the MN. A description of PMIP is made in an Internet Engineering Task Force (IETF) publication entitled “Proxy Mobile IPv6”, by S. Gundavelli et al., available at http:/www3.tools.ietf.org/html/draft-ietf-netlmm-proxymip6-01. Another description may be found in US Patent Application no. 2004/0013116, “Method of providing mobile IP functionality for a non mobile IP capable mobile node and switching device for acting as a mobile IP proxy”, to Greis et al.
FIG. 1 (Prior Art) show a Proxy Mobile IP (PMIP) network 100, consistent with the two foregoing references. The network 100 comprises three subnetworks owned by three distinct operators A, B and C. An access network 110 of operator A comprises a local mobility anchor (LMA) 120, sometimes called local mobility agent, and two media access gateways (MAG) MAG1 and MAG2, which are also sometimes referred to as proxy mobile agents, and which provide PMIP support to MNs. Mobile nodes, for example MN1, MN3 and MN2, are subscribed in the subnetworks of operators B and/or C, but are currently located within the access network 110 of operator A. The LMA is used within operator A's subnetwork to manage local mobility. In an exemplary fashion, MN1 and MN3 are connected to MAG1 and MN2 is connected to MAG2. The MNs may be connected to the MAGs directly or through access points (not shown), which may be wireless access points. Of course, those skilled in the art will recognize that the subnetworks of each operator may comprise a plurality of MAGs and LMAs. Also, the subnetworks would comprise supplementary nodes such as routers, home agents, foreign agents, databases, and the like. Those supplementary nodes are not depicted in FIG. 1 for ease of the description of the problems present in the prior art.
When a given MN attaches to a domain that supports PMIP, it sends an access request, possibly through an access point, which arrives at a MAG. The MAG sends information about the access request to a home agent of the MN. The home agent sends information regarding a home prefix of the MN to the MAG. The MAG advertises this prefix on a link to the MN. This makes the MN act as if the MAG was its home agent. The MAG sends a Proxy Binding Update (PBU) message to the LMA with its own address, called the proxy Care-of Address (pCoA), to be used as a care-of address of the MN. The LMA stores in a binding cache the pCoA and a home address of the MN, the pCoA being used as an identity of the MAG that currently provides access to the MN. If the MN is roaming, implying that the LMA is not part of the home domain for the MN, the LMA builds a regional care-of address (rCoA) and sends the rCoA to the home domain of the MN, thereby making the home domain forward traffic intended to the MN as per the Mobile IP protocol. In a first global mobility process, a packet intended for the MN is sent from the home domain through the LMA by use of the rCoA. Then, in a second local mobility process, the LMA encapsulates this packet and tunnels it to the MAG by use of the pCoA. The MAG receives this packet, decapsulates it, and sends it to the MN. Packets originating from the MN are sent through the MAG to the LMA and then to their destination addresses.
Two MNs that may be attached to same MAG or to distinct MAGs under the same LMA may need to communicate. For example, referring again to FIG. 1, MN1 and MN2 may communicate with each other. When PMIP is used, the two MNs need to use a sub-optimal path leading from a first MAG to the LMA and then to a second MAG, even if there is a shorter direct path between the two MAGs. If two MNs are connected to the same MAG, for example MN1 and MN3 of FIG. 1, which are both connected to MAG1, packets exchanged therebetween still need to transit through the LMA 120. This leads to unnecessary wastage of bandwidth on the links between the MAGs and the LMA, these links usually having limited bandwidth and being costly to operate.